1. Field of the Invention:
The present invention generally relates to matrix panels and their manufacture, and, more particularly, is concerned with the apparatus and method for manufacturing thin film electroluminescent (TFEL) panels.
2. Description of the Related Art:
In recent years, there has been a substantial demand to visually display information. Computers, data analyzers, plotters, radar apparatus, and avionics equipment are only a few of the many electronic devices which involve the visual display of information. Many types of electronic components have been utilized to accomplish visual display of information. One type has been thin film electroluminescent matrix displays (TFEL).
Such display panels comprise generally a transparent panel surface upon which is situated several very closely spaced, parallel, elongated, narrow, and electrically separate transparent conductors. A thin film transparent dielectric is then deposited over the conductor pattern. Upon this surface is deposited a phosphor substance which will emit visible light when subjected to the proper electric potential. Covering these phosphors is yet another thin film of transparent dielectric. Upon this upper dielectric surface, a series of very closely spaced, parallel, elongated, narrow, and electrically separate similar conductors are situated. The longitudinal axis of this upper set of conductors is typically perpendicular to the longitudinal axis of the lower set of conductors. This configuration forms essentially a tight mesh pattern of conductors separated by voltage sensitive phosphors. When the appropriate voltage is applied between a particularly selected pair of conductors, one from the upper conductor pattern and one from the lower conductor pattern, the intermediate phosphors will radiate and the visual display is accomplished within the area intersected by the two conductors.
The physical dimensions of a TFEL matrix display are variable, but typically the transverse dimension of and the perpendicular distance between the parallel conductors is several orders of magnitude smaller than the longitudinal dimension of the conductors There have been several methods used to construct such a pattern of very closely spaced, parallel, elongated, narrow, and electrically separate conductors, but the predominant method has been to deposit a thin film of conductive material upon the desired surface, which then is covered by a thin film of photoresist material. This photoresist is then subjected to a masked light source so that the incident light pattern corresponds to the desired conductor pattern. Typically, one of several etching processes are performed with the end result being a series of elongated electrically separate and parallel conductors being formed upon the surface. This thin film conductor deposition with its photoresist exposure and etching process is commonly used for matrix panel manufacture along with many other applications.
While this process, or variations of it, have been used extensively for matrix panel manufacture, it does have serious drawbacks. One major drawback is the amount of time required to make the several thin film depositions, the light exposure and the several etching operations. Thus, the conventional method requires a substantial expenditure of labor and the use of costly equipment. Another drawback is the tendency for the several etching operations to have a deleterious effect upon the dielectrics and the phosphors within the display panel. Immersing the panel in an etching solution to remove the photoresist and the appropriate portions of the thin conductor film can affect the dielectric materials and the phosphors located within the panel itself.
During the protracted experimentation leading up to the discovery of this invention, one alternative to this invention and the conventional method was attempted but found to be largely unsatisfactory. The attempt was to create a mask, used to facilitate the selective and patterned deposition of the conductor film. The mask was prepared by using the well-known and oft-used photoresist exposure and etching processes to etch interstices in a thin metal sheet. This type of etched thin metal sheet mask has been found to be largely unsatisfactory when the interstices are relatively long in comparison with the width of the remaining thin metal strips separating them. Such masks lack the requisite rigidity and durability needed in the elongated members separating the interstices. Another drawback of such masks is that they are relatively difficult, expensive and time consuming to manufacture.
Another device for manufacturing matrix panels has been disclosed in the reference text by L. E. Tannas Jr. entitled Flat Panel Displays and CRTs, published in 1985 by Van Nostrand Reinhold Company, New York, N.Y., which text is incorporated by reference and made an integral part of this application. Section 8.4.10 of that text, entitled "Electrode Definition", page 263-4, teaches the use of a Kovar mask in the electrode deposition process. The Kovar mask disclosed and shown in FIG. 8.31 on page 264 includes bridges over the interstices of the mask. These bridges tend to create a shadow which may result in non-uniform material deposition along the length of the conductor.
Consequently, a need exists for improvements in the process of and apparatus for depositing several parallel and elongated conductors for a matrix panel which will result in increased levels of conductor uniformity, device reliability and simplicity of manufacture, while concurrently resulting in reduced levels of capital investment, time and energy consumption and degradation of the phosphors and dielectrics.
It is therefore an object of the present invention to provide a matrix panel manufacture method which is quicker, cheaper, easier and more reliable than the conventional method.
It is further an object of this invention to provide a matrix panel manufacture method which produces more reliable matrix panels.
It is further an object of this invention to provide an apparatus used for patterned conductor depositions which is more rigid and durable than masks made by the etching process.
It is further an object of this invention to provide an apparatus which eliminates any bridges across the interstices and thereby provides for a more uniform deposition of the material along the length of the conductor.
It is further an object of this invention to provide an apparatus which is cheaper, quicker and easier to manufacture than those manufactured with the photoresist and etching methods.